skb: Add skb_head_is_locked helper function

This patch adds support for a skb_head_is_locked helper function.  It is
meant to be used any time we are considering transferring the head from
skb->head to a paged frag.  If the head is locked it means we cannot remove
the head from the skb so it must be copied or we must take the skb as a
whole.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 14 insertions, 0 deletions

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 988fc49667b..37f539129d8 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -2566,5 +2566,19 @@ static inline bool skb_is_recycleable(const struct sk_buff *skb, int skb_size)
 
 	return true;
 }
+
+/**
+ * skb_head_is_locked - Determine if the skb->head is locked down
+ * @skb: skb to check
+ *
+ * The head on skbs build around a head frag can be removed if they are
+ * not cloned.  This function returns true if the skb head is locked down
+ * due to either being allocated via kmalloc, or by being a clone with
+ * multiple references to the head.
+ */
+static inline bool skb_head_is_locked(const struct sk_buff *skb)
+{
+	return !skb->head_frag || skb_cloned(skb);
+}
 #endif	/* __KERNEL__ */
 #endif	/* _LINUX_SKBUFF_H */